28. What is Crossing over? In which Cell division does it take place? Explain its significance.

29. What is food adulteration? What is Biodiversity.

30. It was diagnosed that body of a patient has lost its power of fighting any infection. Name the disease the patient has been suffering from. What type of microbe is responsible for this disease? How does it spreads from one person to another? Suggest two methods to prevent this disease.